Thyroidism

Who should be screened for hypothyroidism

• Screen in women trying to become pregnant who have family hx

• Women over the age of 30, women with T1DM or other autoimmune dx

• American Thyroid Association: women and men >35 yrs q 5 years

Drugs that can cause hypothyroidism

• Radioiodine, iodine, lithium, amiodarone

Primary vs secondary hypothyroidism

• Primary: failure of thyroid to secrete hormone

• Secondary: failure of anterior pituitary

Signs and sx of hypothyroidism

• Dry skin, cold intolerance, weight gain, weakness, muscle cramps, course skin/hair, puffy face, bradycardia

TSH is elevated, free T4 is low

Primary hypothyroidism

TSH is elevated, free T4 is normal

• Subclinical hypothyroidism in asymptomatic.

• Do not treat unless sx, goiter, or previous hx

• However, we will treat in pregnancy

How to screen for secondary hypothyroidism

• Will not see high TSH

• Will only see the signs and sx

• Treat with levothyroxine and monitor trtmnt with free T4 levels

Levothyroxine initial and maintenance dosing

• 1.6 mcg/kg/day initial

• Once TSH levels are normal, 50-200 mcg/day

• Lower doses in elderly

• 12.5-25 mcg for those with cardiac risks

Monitoring levothyroxine treatment

• Titrate to obtain normal TSH, increase 25-50 mcg increments

• Retest TSH, free T4 in 4-8 weeks, retest until TSH normal

  • Then 6 mo after that, then annually

• Hold off on daily dose until after labs taken

Levothyroxine administration

• Take with water 30-60 mins b4 breakfast or 4 hours after last meal

• Take 4 hrs apart from meds that may impact abs

Adverse effects of levothyroxine

• Indicates dose is too high

• Palpitations, anxiety, angina, weight loss, tachycardia, diarrhea, afib, bone loss

Low TSH, high free T4

Primary hyperthyroidism

High TSH, high free T4

Secondary hyperthyroidism

Graves’ Disease

• Autoimmune; IgG activates TSH receptor

• Iodine-123 scan: diffuse increased uptake by thyroid

• Ophthalmopathy

Toxic adenoma

• Benign mass on thyroid, secretes thyroid hormone autonomously

• Takes up iodine-123 on scan

Drugs that can cause hyperthyroidism

Amiodarone, iodine, lithium

Hyperthyroidism sx

Weight loss (w/ preserved appetite), heat intolerance, nervous/anxiety, fatigue, tremor, increased bowel movements, palpitations, afib, hypertension

Hyperthyroidism sx in elderly

• Worsening left ventricular fxn, afib, depression, fatigue, hypokinesia, weight loss, poor appetite, constipation

Methimazole

• Blocks synthesis of thyroid hormone by interfering with thyroid peroxidase enzyme

• THE first choice drug EXCEPT in the first trimester of pregnancy

• Monitor w/ CBC, white ct w/ differential, LFTs

Methimazole dosing

• Initial: 10-20 mg daily

• 5-10 mg daily maintenance

Propylthiouracil

• Blocks synthesis of thyroid hormone by interfering with thyroid peroxidase enzyme

• Recommended for the first trimester of pregnancy, then switch to methimazole

• Monitor w/ CBC, white ct w/ differential, LFTs

Propylthiouracil dosing

• Initial: 50-150 mg TID

• 50 mg 2-3x/day maintenance

Drug efficacy monitoring in hyperthyroidism

• Measure free T4 at about 4weeks, adjust prn

  • Serum TSH will not respond quickly

• Monitor q 4-8 weeks until euthyroid, then every 2-3 months

Side effects of methimazole and PTU

• Rash, liver dysfxn, arthalgia, transient leukopenia, agranulocytosis

PTU and liver toxicity

• Monitor for sx of liver injury, especially in first 6 months

Radioactive Iodine

• Used in Graves’ dx

• Thyroid gland takes up I-131 and is destroyed

• Will need levothyroxine treatment after